Investigation of the Fuel Distribution in a Shockless Explosion Combustor

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Fatma Cansu Yücel ◽  
Fabian Habicht ◽  
Alexander Jaeschke ◽  
Finn Lückoff ◽  
Kilian Oberleithner ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Concentration Profile ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Transport Processes ◽  
Turbulent Pipe Flow ◽  
Tunable Diode Laser ◽  
Fuel Concentration ◽  
Auto Ignition ◽  
Fuel Profile

Abstract Shockless explosion combustor (SEC) is a promising concept for implementing pressure gain combustion into a conventional gas turbine cycle. This concept aims for a quasi-homogeneous auto-ignition that induces a moderate rise in pressure. Since the ignition is not triggered by an external source but driven primarily by chemical kinetics, the homogeneity of the auto-ignition is very sensitive to local perturbations in equivalence ratio, temperature, and pressure that produce undesired local premature ignition. Therefore, the precise injection of a well-defined fuel profile into a convecting air flow is crucial to ensure a quasi-homogeneous ignition of the entire mixture. The objective of this work is to demonstrate that the injected fuel profile is preserved throughout the entire measurement section. For this, two different control trajectories are investigated. Optical measurement techniques are used to illustrate the effect of turbulent transport and dispersion caused by boundary layer effects on the fuel concentration profile. Results from line-of-sight measurements by tunable diode laser absorption spectroscopy indicate that the transport of the fuel-air mixture is dominated by turbulent diffusion. However, comparisons to numerical calculations reveal the effect of dispersion toward the bounds of the fuel concentration profile. The spatially resolved distributions of the fuel concentration inside the combustor gained from acetone planar laser induced fluorescence (PLIF) replicates a typical velocity distribution of turbulent pipe flow in radial direction visualizing boundary layer effects. Comparing both methods provides deep insights into the transport processes that have an impact on the operation of the SEC.

Investigation of the Fuel Distribution in a Shockless Explosion Combustor

2020 ◽  
Author(s):  
Fatma Cansu Yücel ◽  
Fabian Habicht ◽  
Alexander Jaeschke ◽  
Finn Lückoff ◽  
Kilian Oberleithner ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Concentration Profile ◽  
Optical Measurement ◽  
Turbulent Transport ◽  
Measurement Techniques ◽  
Transport Processes ◽  
Turbulent Pipe Flow ◽  
Tunable Diode Laser ◽  
Fuel Concentration ◽  
Fuel Profile

Abstract Shockless explosion combustion is a promising concept for implementing pressure gain combustion into a conventional gas turbine cycle. This concept aims for a quasi-homogeneous autoignition that induces a moderate rise in pressure. By this, considerable losses due to entropy generation by inherent shock waves of detonation-based concepts can be avoided. Since the ignition is not triggered by an external source but driven by chemical kinetics only, the homogeneity of the autoignition is very sensitive to local perturbations in equivalence ratio, temperature, and pressure that produce undesired local premature ignition. Therefore, the precise injection of a well-defined fuel profile into an convecting air flow is crucial to ensure a quasi-homogeneous ignition of the entire flammable mixture. The objective of this work is to demonstrate that the injected fuel profile is preserved throughout the entire measurement section. For this, two different control trajectories are investigated. Optical measurement techniques are used to illustrate the effect of turbulent transport and dispersion caused by boundary layer effects on the fuel concentration profile inside the combustor. Results from line-of-sight measurements by tunable diode laser absorption spectroscopy indicate that the transport of the fuel-air mixture is dominated by turbulent diffusion. However, comparisons to numerical calculations reveal the effect of dispersion towards the bounds of the fuel concentration profile. The spatially resolved distributions of the fuel concentration inside the combustor gained from acetone planar laser induced fluorescence replicates a typical velocity distribution of turbulent pipe flow in radial direction visualizing boundary layer effects. Comparing both methods provide deep insights into the transport processes that have an impact on the operation of the shockless explosion combustor.

High Intensity Focused Ultrasound (HIFU) Transducer Characterization Using Acoustic Streaming

2007 ◽  
Author(s):  
Prasanna Hariharan ◽  
Ronald A. Robinson ◽  
Matthew R. Myers ◽  
Rupak K. Banerjee
Keyword(s):  
High Intensity ◽  
Focused Ultrasound ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Acoustic Streaming ◽  
Acoustic Power ◽  
High Intensity Focused Ultrasound ◽  
Medical Ultrasound ◽  
Intensity Field ◽  
Streaming Velocity

A new, non-perturbing optical measurement technique was developed to characterize medical ultrasound fields generated by High Intensity Focused Ultrasound (HIFU) transducers using a phenomenon called ‘acoustic streaming’. The acoustic streaming velocity generated by HIFU transducers was measured experimentally using Digital Particle Image Velocimetry (DPIV). The streaming velocity was then calculated numerically using the finite-element method. An optimization algorithm was developed to back-calculate acoustic power and intensity field by minimizing the difference between experimental and numerical streaming velocities. The intensity field and acoustic power calculated using this approach was validated with standard measurement techniques. Results showed that the inverse method was able to predict acoustic power and intensity fields within 10% of the actual value measured using standard techniques, at the low powers where standard methods can be safely applied. This technique is also potentially useful for evaluating medical ultrasound transducers at the higher power levels used in clinical practice.

scholarly journals Validation of farm-scale methane emissions using nocturnal boundary layer budgets

2015 ◽  
Vol 15 (15) ◽  
pp. 21765-21802 ◽  
Author(s):  
J. Stieger ◽  
I. Bamberger ◽  
N. Buchmann ◽  
W. Eugster
Keyword(s):  
Boundary Layer ◽  
Nocturnal Boundary Layer ◽  
Methane Emissions ◽  
Emission Factors ◽  
Transport Processes ◽  
Tethered Balloon ◽  
Near Surface ◽  
Time Space ◽  
Farm Scale ◽  
Balloon System

Abstract. This study provides the first experimental validation of Swiss agricultural methane emission estimates at the farm scale. We measured CH4 concentrations at a Swiss farmstead during two intensive field campaigns in August 2011 and July 2012 to (1) quantify the source strength of livestock methane emissions using a tethered balloon system, and (2) to validate inventory emission estimates via nocturnal boundary layer (NBL) budgets. Field measurements were performed at a distance of 150 m from the nearest farm buildings with a tethered balloon system in combination with gradient measurements at eight heights on a 10 m tower to better resolve the near-surface concentrations. Vertical profiles of air temperature, relative humidity, CH4 concentration, wind speed and wind direction showed that the NBL was strongly influenced by local transport processes and by the valley wind system. Methane concentrations showed a pronounced time course, with highest concentrations in the second half of the night. NBL budget flux estimates were obtained via a time–space kriging approach. Main uncertainties of NBL budget flux estimates were associated with instationary atmospheric conditions and the estimate of the inversion height zi (top of volume integration). The mean NBL budget fluxes of 1.60 ± 0.31 μg CH4 m-2 s-1 (1.40 ± 0.50 and 1.66 ± 0.20 μg CH4 m-2 s-1 in 2011 and 2012, respectively) were in good agreement with local inventory estimates based on current livestock number and default emission factors, with 1.29 ± 0.47 and 1.74 ± 0.63 μg CH4 m-2 s-1 for 2011 and 2012, respectively. This indicates that emission factors used for the national inventory reports are adequate, and we conclude that the NBL budget approach is a useful tool to validate emission inventory estimates.

A Comparative Study on Hydraulic Bulge Testing and Analysis Methods

2008 ◽  
Author(s):  
Eren Billur ◽  
Muammer Koc¸
Keyword(s):  
Flow Stress ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Material Behavior ◽  
Biaxial Stress ◽  
Dome Height ◽  
Bulge Test ◽  
Analysis Methods ◽  
Bulge Testing ◽  
Hydraulic Bulge

Hydraulic bulge testing is a material characterization method used as an alternative to tensile testing with the premise of accurately representing the material behavior to higher strain levels (∼70% as appeared to ∼30% in tensile test) in a biaxial stress mode. However, there are some major assumptions (such as continuous hemispherical bulge shape, thinnest point at apex) in hydraulic bulge analyses that lead to uncertainties in the resulting flow stress curves. In this paper, the effect of these assumptions on the accuracy and reliability of flow stress curves is investigated. The goal of this study is to determine the most accurate method for analyzing the data obtained from the bulge testing when continuous and in-line thickness measurement techniques are not available. Specifically, in this study the stress-strain relationships of two different materials (SS201 and Al5754) are obtained based on hydraulic bulge test data using various analysis methods for bulge radius and thickness predictions (e.g., Hill’s, Chakrabarty’s, Panknin’s theories, etc.). The flow stress curves are calculated using pressure and dome height measurements and compared to the actual 3-D strain measurement from a stereo optical and non-contact measurement system ARAMIS. In addition, the flow stress curves obtained from stepwise experiments are compared with the ones from above methods. Our findings indicate that Enikeev’s approach for thickness prediction and Panknin’s approach for bulge radius calculation result in the best agreement with both stepwise experiment results and 3D optical measurement results.

Detecting Transition in Flat Plate Flow With Laser Interferometric Vibrometry (LIV)

2016 ◽  
Author(s):  
Pascal Bader ◽  
Wolfgang Sanz ◽  
Johannes Peterleithner ◽  
Jakob Woisetschläger ◽  
Franz Heitmeir ◽  
...  
Keyword(s):  
Flat Plate ◽  
Measurement Techniques ◽  
Transitional Zone ◽  
Transport Processes ◽  
Transitional Region ◽  
Test Cases ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Measurement Results ◽  
Laser Interferometric

Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. Relaminarization from turbulent to laminar flow may also occur. The state of the boundary layer is important since it strongly influences transport processes like skin friction and heat transfer. It is therefore vitally important for the designer to understand the process of laminar-to-turbulent transition and to determine the position of transition onset and the length of the transitional region. In order to better understand transition and relaminarization it is helpful to study simplified test cases first. Therefore, in this paper the flow along a flat plate is experimentally studied to investigate laminar-to-turbulent transition. Measurements were performed for the different free-stream velocities of 5 m/s and 10 m/s. Several measurement techniques were used in order to reliably detect the transitional zone: the Preston tube, hot wire anemometry, thermography and Laser Interferometric Vibrometry (LIV). The first two measurement techniques are extensively in use at the institute ITTM and by other research groups. They are therefore used as a reference for validating the LIV measurement results. An advantage of the LIV technique is that it does not need any seeding of the fluid and that it is non-intrusive. Therefore this measurement technique does not influence the flow, and it can be used in narrow flow passages since there is no blockage, in contrast to probe-based measurement techniques. Further to the measurements, computational simulations were performed with the Fluent® and CFX® codes from ANSYS®, as well as with the in-house code Linars. The Menter SST k-ω turbulence model with the γ-ReΘ transition model was used in order to test its capability to predict the laminar-to-turbulent transition.

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